Tracking Ocean Currents

Radioactive tritium became a perfect marker for tracking ocean
water §. Scientists sampling North Atlantic water found that
tritium released into the atmosphere before the 1962 nuclear test
ban treaty, mixed downward by 1973. By 1980, the same tritium
had moved into deep areas off Florida. The water had taken about
20 years to travel 3000 miles (4800 km) through the sea at an
average speed of less than half a mile a day, about half the
speed of a snail §.

Turbidity currents sweep sediment from shallow water to deep

Not all currents are predictable. Turbidity currents are
submarine avalanches. Sediments settle and accumulate in shallow
areas like the edges of the continental shelf and slope. Often
triggered by an earthquake, they can spill down the continental
slope into deep water. Fast turbidity currents carrying
suspended sediments may spread over wide areas §.

Transatlantic telegraph cables snapped from north to south over
thirteen hours in 1929, when an earthquake off New England sent
sediments slumping and sliding. Scientists calculated that the
resulting turbidity current traveled 25-35 miles per hour (40-55
kph), and covered an area slightly larger than Maine and
Connecticut §.